1. Field of the Invention
The present invention relates to a continuous variable valve lift (CVVL) device and, more particularly, to a CVVL device in which a valve has simultaneously variable lift time and distance depending on the low-/high-speed operating range of an engine.
2. Description of the Related Art
As for an engine, a camshaft is rotated by a rotating force transmitted from a crank shaft, and an intake valve and an exhaust valve are reciprocated up and down with regular timing by cams of the camshaft. Thereby, intake air is supplied to a combustion chamber, and then combustion gas is exhausted. In this process, a fuel-air mixture is compressed and exploded to generate power.
At this time, a device that can continuously vary the lift distance of a valve according to an operating speed of the engine is called a continuous variable valve lift (CVVL) device.
Hereinafter, a conventional CVVL device will be described in detail with reference to the attached drawings.
FIG. 1 is a schematic view illustrating the configuration of a conventional continuous variable valve lift (CVVL) device.
The conventional CVVL device illustrated in FIG. 1 is disclosed in Japanese Patent Application Publication No. 2007-218242. This CVVL device includes a drive cam 4 installed on a cam shaft 2, a rocker arm 12 rocking in contact with the drive cam 4, a driving arm 19 driving a valve 5 in cooperation with the rocking arm 12, a variable arm 13 rotating the driving arm 19 around a rocking shaft of the rocking arm 12, an actuator driving the variable arm 13, and a cam module installed between the rocker arm 12 and the driver arm 19.
The rocking arm 12 and the variable arm 13 are relatively rotatably supported on a common control shaft 10. The driving arm 19 is connected to the variable arm 13 at a base end thereof, and is provided with a driving part 20 driving a rocker arm 6 at a leading end thereof. Further, the cam module includes cam faces 15a and 15b formed on the rocking arm 12, a cam follower 22 supported at a middle part of the driving arm 19. An initial position of the driving arm 19 is configured to be changed with respect to the rocking arm 12 by the rotation of the driving arm 19.
In the conventional CVVL device configured as described above, when the drive cam 4 is rotated in a counterclockwise direction in the state illustrated in FIG. 1, an end of the rocking arm 12 (right-hand end in FIG. 1) is rotated so as to approach the driving arm 19. After the end of the rocking arm 12 is contacted with the driving arm 19, the rocker arm 6 is pressed together, and thus the valve 5 is opened.
At this time, when the variable arm 13 is rotated in a counterclockwise direction in the state illustrated in FIG. 1, the driving arm 19 comes into contact with the rocker arm 6 at a middle portion compared to the state illustrated in FIG. 1, and thus comes closer to the end of the rocking arm 12. In this state, when the drive cam 4 is rotated, the end of the rocking arm 12 presses the driving arm 19 earlier than usual. Thus, the valve 5 is not only opened at an earlier point of time but also has a longer lift distance.
Thus, the conventional CVVL device illustrated in FIG. 1 makes it possible to control the lift time and distance of the valve according to the speed of the engine.
However, the conventional CVVL device configured as described above is configured to control the lift distance of the valve 5 by rotating the part, i.e. the driving arm 19, pressing the rocker arm 6. Thus, an outer surface of the driving arm 19 must be precisely machined so as to prevent the valve 5 from being lift when only the driving arm 19 is rotated. As a result, it is difficult to machine the driving arm 19.
Further, in the conventional CVVL device configured as described above, the opening time of the valve 5 becomes fast when the lift distance of the valve 5 becomes long, and the opening time of the valve 5 becomes late when the lift distance of the valve 5 becomes short. For this reason, the opening time of the valve 5 cannot be made constant regardless of the lift distance of the valve 5.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.